Level measurement forms a central part in many industrial applications. Level measurement data is for example used for industrial process control and/or automation. Various level measurement devices are presently available on the market.
Some devices use mechanical floats or displacers mounted on a cable or rod inside the container. The position of these floats is used to determine the level of the liquid. Magnetostrictive, resistance or cable tension sensing technologies are used to determine the position of the float. Mechanical floats and displacers often require significant maintenance and are subject to material buildup errors. They often require physical entry into a container in order to clean and/or repair the device.
In many branches of industry high standards of hygiene, cleanliness and cleanability are required. Standardized cleaning and sterilization methods are applied to fulfill these requirements. Widely used methods are Cleaning in Place (CIP) or Sterilization in Place (SIP). Cleaning and/or sterilization can be carried out with automated or manual systems via various procedures on the site in a reliable and repeatable process that meets the stringent hygiene regulations demanded by biotechnology and pharmaceutical industries. Some systems include spray balls which can be permanently installed inside containers to apply liquid cleaners, water, detergents, steam or other cleaning or sterilization agents into closed containers. This has the advantage that containers do not need to be opened and exposed to the environment for cleaning and/or sterilization purposes.
There is a great reluctance to use mechanical floats, because they cannot be easily cleaned using these method.
Time of flight radar techniques have been used to determine the position of the surface of a product in a container. Corresponding level measurement devices comprise a conductive probe that extends into the container. The probe is connected to sensor electronics comprising means for generating and sending short electromagnetic pulses down the probe and means for reception of echoes of the pulses reflected at a surface of the product. The level of the product is determined based on a measurement of a time of flight needed for a pulse to travel down the probe and its echo to return. Such devices are for example the Guided Radar Transmitters Levelflex FMP 40, sold by the applicant.
In order to measure levels near the bottom of the container, the probe preferably extends far down into the container, leaving only a small gap between the tip of the probe and the adjacent container wall. When spray balls are applied, it is possible, that a bottom side of the probe facing away from the spray ball cannot always be successfully cleaned and/or sterilized by spray balls, thus allowing deposits to build up in this area.
In existing devices the probe is an integral part of the device and is for example welded or threaded to a process connection for mounting the device on the container. In order to clean and/or sterilize the tip of the probe, the entire device may have to be taken out of the container, thus leaving an opening in the container, through which the interior of the container is exposed to the environment. In addition it might be necessary during maintenance of the device, to take the device out of the container. This is not acceptable in many biotechnological or pharmaceutical applications.